


The darker side of magic

by theonetruenorth



Category: Shadowhunters (TV), The Mortal Instruments Series - Cassandra Clare
Genre: BAMF Magnus Bane, Blood and Violence, Dark Magic, Embedded Images, Insecure Magnus Bane, M/M, Necromancy, Powerful Magnus Bane, Torture
Language: English
Status: Completed
Published: 2017-05-07
Updated: 2017-05-07
Packaged: 2018-10-29 02:09:02
Rating: Mature
Warnings: Graphic Depictions Of Violence
Chapters: 1
Words: 3,632
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10844292
Author URL: https://archiveofourown.org/users/theonetruenorth/pseuds/theonetruenorth
Summary: Alec is still next to him, looking at Magnus with clever eyes and Magnus can practically see the cogwheels turning in his head.“You have a plan.” Alec's quiet voice is only for Magnus’ ears to hear. “I know that look. It’s your‘I’m going to have to something I don’t want to do’face.”





	The darker side of magic

**Author's Note:**

> Otherwise known as “The reasons why Magnus is the High Warlock” or “Omfg, we’ve been using him as we please while he can do THIS?”
> 
> Because I am annoyed that the group treats Magnus as a glorified pet warlock while he doesn’t get the respect that he deserves. Possible trigger warning for blood and torture, just to be on the safe side.
> 
> (Parts of this fic were inspired by “The Witcher 3″ game. If you played it you’ll know what I mean.)

Magnus looks at Jace, who is currently trying to break through the barrier by sheer force, and shakes his head at the blond boy. His gaze shifts towards Marcus who is sprawled on the floor. The unseeing eyes and the way they stare into nothingness makes him shiver, and he already dreads what is to happen soon.

“That’s enough,” he calls out, making Jace turn to him, along with Alec and Isabelle. “You won’t escape that way.” Magnus looks at the body again. “It’s not possible to break through it.”

“Then how do we get out?” Alec asks, his attention back on the red barrier of energy that cut them off as soon as they entered the room. They had been chasing after a lead. That lead was Marcus, a rogue warlock who worked for demons and had information they needed. The same warlock who lay dead on the floor.

Magnus thought he was doing the right thing, going after one of his people who turned on his own kind, but now he wishes he hadn’t.

“We don’t.” Magnus sighs, closing his eyes. “It’s a Crimson Oath.”

“So you know the spell.” Izzy steps closer to Magnus and he can see that she practically vibrates with tension. She doesn’t like feeling trapped. “Can you do something about it?”

He shakes his head and the others come closer. They tracked the warlock to an abandoned theater, the building old and in a pitiful state. Some of the furniture is still there and Magnus sits in the chair next to him, after eyeing it for a moment and deciding that it probably wasn’t going to fall apart under him.

“The Crimson Oath is a spell that was designed as one last grand _‘fuck you’_ to a warlock’s enemies. Something to be used when you know you will die and want to take as many as you can with you. You seal it with your own life and the only way to break it is to know a keyword.” Magnus closes his eyes for a second. “Since you’re the only one who knows it and you are dead anyways...”

He doesn't finish but he doesn’t really have to. All three of the shadowhunters seem to grasp that they are fucked.

“God dammit!” Jace huffs and stomps off, probably to try to break through the barrier again. Magnus doesn’t really blame him, he would like to take his anger out on something as well, but he feels frozen, unable to move. Izzy takes off after Jace, possibly to try to calm him down.

Alec is still next to him, looking at Magnus with clever eyes and Magnus can practically see the cogwheels turning in his head.

“You have a plan.” Alec's quiet voice is only for Magnus’ ears to hear. “I know that look. It’s your _‘I’m going to have to something I don’t want to do’_ face.”

Despite the bleakness of the situation, Magnus can’t help but snort.

“You know me well, darling,” he says after a moment and Alec shakes his head, coming closer. He ends up standing just between the warlock’s slightly spread knees and Alec cups Magnus’ jaw with both hands, making the older man look up at him.

“Then tell me why you can’t look me in the eyes for more than a second.”

Magnus flinches and would have turned away again if it wasn’t for Alec’s hold on his face. Alec raises one eyebrow at him, as if Magnus had just proven his point.

“Because I never wanted you to see me like this,” Magnus admits, the words sounding forced, like he has to physically push them out of his throat. “To witness this side of me.”

“Magnus.” Alec sounds worried as he runs the fingers of one hand through Magnus’ hair; soft and silky, despite the product in it. Magnus closes his eyes and leans more into the touch. “Please, just tell me what’s going on.”

“Marcus was the only one who knew the keyword.” Magnus looks towards the dead warlock again. He wishes the man was alive, so that he could kill him himself. He can feel anger - hate, even - taking hold of him as he thinks of his dead charge. Marcus’ betrayal is forcing Magnus to reveal the parts of himself he would rather leave buried. “I am going to make him tell us what it is.”

“Magnus, the man is dead,” Alec says carefully, frowning at the words like he’s trying to decide if Magnus hit his head or something. “He’s not going to tell you anything now.”

“His vocal cords are intact,” Magnus replies, his tone emotionless and clinical, already trying to distance himself from what he’s about to do. “He’ll talk.”

Magnus sees the exact moment that understanding dawns on Alec. He opens his mouth to say something but freezes. His hand twitches, pulling at Magnus’ hair for a second, but he immediately gentles his hold.

“Necromancy,” Alec whispers and Magnus looks him in the eyes, waiting for his reaction. “You’re talking about necromancy.”

Magnus can hear the apprehension in his voice, the quiet undertone of fear of the unknown. It almost physically hurts him.

“We’re short on time,” Magnus explains slowly, trying to find the right words. “The Oath will hold until we’re all dead. Even if we decided to be better than this and die within it, what about the sacrifices?” Magnus reminds him of the three kidnapped children, mundane and Downworlders alike, that Marcus took from their parents as an offering for the demons he worked with. They still haven’t found their location, which is the reason they were tracking Marcus in the first place. “If we don’t get to them soon, they are as good as dead.”

It’s a little bit of a dirty trick, really. Magnus knows that the mention of children will push Alec into a decision, and he’s proven right when Alec’s eyes harden a little, the earlier fear replaced by determination.

He has a moment to prepare as Alec goes off to tell Jace and Izzy about their solution. He can hear Jace protesting, saying that there must be another way. Alec shuts him up by asking if he has any idea, other than hitting the barrier until he breaks both of his hands, than he’s free to share it with the rest of the group.

Magnus stands over Marcus’ body, trying to see him as just another enemy instead of an old acquaintance and he fails. All he sees is the man he has known for almost eighty years now. The man who once came to his home, completely plastered on absinthe, seeking relationship advice due to some Seelie girl that dumped him. Magnus taught him how to use healing magic to repair nerve damage, so that he could help his mundane friend who had an accident and lost the use of their arm. Magnus can’t look at his body and see a traitor, even though that’s what he is. He took children and used them as demon sacrifices and then kidnapped more to do it again. Whatever his reasons were, Magnus doesn’t think human sacrifices could ever be justified.

He sighs and snaps his fingers and a rune array carves itself into the floor underneath the body, long lines scratching into the wood with a hair-raising sound. He takes off his coat - leaving him in the burgundy silk shirt he wore underneath - as well as his rings and bracelets, handing them to Izzy for safekeeping.

“Are you sure?” Alec asks as he comes to stand beside him, looking down at Marcus’ body and the markings under it. “Are you sure you want to do this?”

“No.” Magnus chuckles, but it’s a humorless, ugly sound. “But there is no other way.”

“Then why are you shaking?”

Magnus looks down at his hands and sure enough, he’s trembling so hard it looks like he has one of those mundane diseases.

“This is going to change everything,” he whispers, trying to will his limbs into obedience and make them steady. It’s not working. “You’ve never seen some of the things that I can do.”

“I know you. I know what kind of person you are,” Alec says gently, carefully, taking Magnus’ hands in his own, not paying attention to the way Magnus flinches at the contact. “It’s going to be alright.”

“No, it won’t.” Magnus shakes his head, finally raising his gaze up from their joined hands and looking at Alec. The nephilim’s eyes are wary but he doesn’t see fear in them.

Not yet.

“I’ve been here before,” the warlock whispers, trying to commit to memory the way Alec looks at him, with trust and love shining through his eyes, knowing that it’s the last time he’ll see it. “Others have seen me do this and nothing is ever the same after that. You might say it’s okay now, you might even believe it - but afterwards things always change. There’s always fear, or hate, or repulsion. You won’t be able to look into my eyes and not see the demon half of me.”

“You sound like you’re already saying goodbye.” Alec sounds angry and his hands squeeze Magnus’ a little harder. “Like you already know what I will say or think.”

“Let’s just get this over with.”

“Magnus, we’re not done,” Alec hisses but Magnus drops his hands and shakes his head.

“We don’t have time for this right now.”

Alec looks like he wants to protest, his jaw working as the words try to burst free from him.

“Fine,” the nephilim finally agrees. “Later, then.”

“Later,” Magnus replies, even though he knows it’s not going to happen. Alec won’t stay with him after all is said and done.

After requesting one of Jace’s daggers, he orders the three shadowhunters away - as far as they can go within the confines of the barrier. It’s only partially because he’s afraid of magical backlash reaching them, but some part of him just wants them to not look, to be as far away as possible.

“Whatever happens, you don’t interfere,” he tells them, assuming his position above the body, and then looks at them. “Are we clear?”

All three of them nod. Magnus sighs and then lets his magic loose.

He begins chanting the spell and can already feel the temperature in the room dropping rapidly, all the heat being slowly sucked out of it and powering the spell. With the corner of his eye, Magnus can see Izzy putting on his coat, covering her exposed form. The room grows a little darker too, as if even the light is consumed for more power.

Magnus slices his left palm open - he can hear Alec’s noise of protest but pays it no attention - and holds it over Marcus’ head, letting his blood spatter over the corpse’s open mouth. He tosses the dagger away and his magic heals the cut without his conscious thought. He waits for a moment, still chanting, waiting for his blood to spread through the body, the magic pushing it along the tissues, almost like an infection.

The room grows even colder but Magnus doesn’t register it. He can feel the new blood pumping through Marcus’ body, can feel the way it sings to him when he’s like this, tuned into his own life force rushing through the previously dead veins, possessing it from the inside. He drops to his knees and can feel the moment when his eyes turn white. It somehow makes the whole world sharper, more primal. There’s a frantic whisper from the group - Jace, he thinks - but he can’t understand the words anymore.

Magnus leans over the body and places his left hand over its heart, his right over Marcus’ head. For a moment nothing happens, but Magnus is patient. He knows he has to be. Black mist starts pooling over his hands and, with an inhale of determination, Magnus gathers his magic at the tips of his fingers and shoves them into Marcus’ chest.

The effect is immediate, Marcus’ body seizing up, his back arched into a perfect impression of a upside-down letter ‘u’. Magnus can hear a startled gasp from the direction of the others, but doesn’t look at them. He can’t, not now. Can’t distract himself with their horrified faces.

Marcus is screaming, a tortured yell that is like an acid pouring over his nerves, and Magnus shoves him down until he’s on his back again. Blood pours from the puncture wound on his chest, Magnus’ fingers still deep within it, connecting his magic to the heart and forcing it into beating once more.

“Back with us, Marcus?” Magnus asks, his voice ice cold. His right hand still hovers over Marcus’ head, black mist wrapping over his fingers in angry, violent swirls. “Answer me.”

“S-s-stop!” Marcus stutters out, a little unclear and gravelly, the stiff tongue unable to form the words right. “It h-hurt-s!”

“It should hurt,” Magnus hisses, his hand digging in deeper, tearing another shout from the dead warlock. “Just like you hurt those children.”

“Let m-me g-gooo!” Marcus tries to move away from him, but Magnus’ right hand twitches and stops him effortlessly.

“The Crimson Oath, you traitor.” Magnus tilts his head as he looks at his old charge. He can feel himself slipping and fights it, fights the feeling of blackness creeping into his mind. It’s been so long since he had to do this and it’s a feeling he could never forget. His demon blood calls out to him and craves the power that the blackness can give him. “Give me the keyword.”

“N-no.”

“Tell me.”

“F-fuck you, M-Magnus!” Marcus’ face twitches into a visage of pure hatred and Magnus really, really doesn’t understand what pushed the other warlock to that point.

It doesn’t matter anymore.

“Tell me!” Magnus shouts, pushing more magic behind his command. The room they are in shakes with the power behind his voice. There’s frost creeping up from the corner of the room, covering all the surfaces with a thin layer of white. Marcus writhes underneath his hand, pain coursing through his veins along with Magnus’ blood, tearing him from the inside.

The old theater has great acoustics, unfortunately. Marcus’ screams of pain fill the space of the room, bouncing off the walls.

“C-clairvoyant!” The dead warlock finally gives in under the stress of pain and magic, the word ripping out of him with great difficulty. The red barrier around the room pulses a couple of times before it shatters with a great booming sound, so loud it’s almost enough to burst eardrums.

The Crimson Oath is broken.

“And the children?” Magnus asks, looking back at Marcus. His voice is aggressive and dominating and he gives Marcus no respite. You couldn’t afford it when commanding the dead - the souls forced back into lifeless bodies didn’t want to co-operate, they had to be subjugated. Marcus’ mouth is stained red and blood pours freely from the wound on his chest. Magnus knows he doesn’t have long before his blood is expelled from the reanimated body and Marcus will be gone. “Speak.”

“N-no more, p-p-please.” Marcus’ voice is quiet, the life once more leaving his eyes and Magnus knows he’s slipping away. He can’t afford it, not yet.

“Speak!” He shouts once more, magic tearing into Marcus’ heart, the brute force that makes it pump kicking up a notch. The body writhes under him, limbs strewn and shaking with pain.

“Ninety-first.” Marcus’ voice is nothing but a croak now, throat torn from all the yelling. “Ab-abandoned station.”

Magnus yanks his hand out of Marcus’ chest as he fades away, but it’s a touch too late and he's caught with the sensation of his life extinguishing again. It feels like ice touching his very core, freezing him from the inside.

The moment he severs the contact, the room grows brighter. The warmth returning like a summer heat wave. Magnus gasps, the white film retreats from his eyes and he stands up. His left arm is covered with dark blood up to his elbow and he magics it away before he stumbles off to a side. He collapses near an ornamental column, facing away from the group of shadowhunters.

He doesn’t know how long he sits there but after some time - seconds, minutes, hours - Magnus feels a hand on his shoulder and he opens his eyes, more than a little warily.

Alec is crouching next to him, looking at him with an expression that is carefully neutral. Magnus can’t read him at all, which is more than surprising - the younger man wears his emotions on his sleeve most of the time.

“Are you okay?” Alec asks, his sharp eyes searching his face for the signs of exhaustion that creep into his bones now. Magnus looks to the side, expecting to see Jace and Izzy there, but they are gone.

“They went to the subway station. I’ll join them in a moment,” Alec says. “Do you have enough magic left to portal back home?”

“I should go with you,” Magnus says, even though he feels his limbs grow heavy with fatigue.

“Magnus, you can hardly stand.” Alec shakes his head. “Go home, rest. I’ll be there as soon as we get the kids back.”

Magnus looks away with a heavy sigh.

“Hey,” Alec calls out to him, his tone soft and quiet. He grabs Magnus’ chin to turn his face back again. “I promise you, I’ll be there.”

Magnus can only nod, too exhausted for words. His head is swimming, his thoughts racing despite the tiredness he’s experiencing. He feels unclean, like his mind had been submerged in a tar pit - overpowering and consuming, blocking out anything else in the world.

He snaps his fingers and a portal appears in front of them. He goes through it, refusing to look back at Alec. He doesn’t want to look at him for what he’s sure is the last time.

Back at the apartment, Magnus doesn’t have any strength left to do anything else but stumble towards the couch and fall onto it, his body refusing to move any further. He falls into an uneasy sleep, interrupted with nightmares that creep up upon him, now that he opened his mind to the darkness.

He doesn’t know how long he sleeps, but it can’t be very long since it’s still night outside and he’s so very tired. At first, Magnus doesn’t understand what woke him up but after a moment of confusion, he realizes it was Alec.

He came back.

Alec is stretching out on the couch next to him, manhandling the now awake warlock until Magnus can lay on top of him, his head resting on Alec’s chest. The nephilim’s arms are wrapped around him, large hands splayed wide over his back, gently petting through the thin layer of his silk shirt.

“You’re here,” Magnus whispers, still half-dazed with sleep, pressing his ear harder against Alec’s chest to listen to the comforting thump-thump of his heart. Alec feels so good, so _alive_ , that it makes his eyes tear up. Magnus knows his emotions are always all over the place after using that kind of magic, but right now the proof of life that is Alec Lightwood is all that he needs.

“Of course I’m here,” Alec says, one of his hands reaching up to cradle the back of Magnus’ skull, holding him close. “Where else would I be?”

Magnus makes a short, unhappy sound and nuzzles harder into Alec’s chest, Alec’s fingers running slowly through his hair.

“The people you mentioned before, who made you feel like this,” Alec whispers, his tone colored with anger but Magnus knows that it’s not directed at him, “I would like to hunt them down.”

“I’m sorry.” Magnus closes his eyes, focusing on the heartbeat underneath his ear, on how steady it is. “I’m so sorry you had to see me like that.”

Alec is quiet for a moment, but his fingers start running through Magnus’ hair again, a slow caress bringing both of them some comfort.

“There were six kids,” Alec eventually says. “ _Six_ , Magnus. We only knew about three. If you had not done what you did, there would be six more sacrifices.”

“And the demons?”

“Dead.” Alec confirms. “We got them all. And it’s all thanks to you. If it wasn’t for you, they would still be free to kill. Not to mention me, Izzy, and Jace would all be dead as well. If you weren’t with us when the Oath sealed off the room...”

Magnus shivers. He doesn’t even want to think about that.

“What about the others? How did they react?”

“Others? You mean Jace and Izzy?”

“Mhm.” Magnus makes a sound of affirmation. He’s getting tired again and he still hasn’t gotten enough sleep to recover from the spell.

“I think they were mostly surprised, really. We all were,” Alec admits. They got used to Magnus doing so much for them that they forgot that Magnus wasn’t just any warlock. He was _the_ High Warlock, capable of performing magic that was beyond the skill of an average practitioner. His magic could be playful and awe-inspiring, but it also could be powerful and destructive.

Alec doesn’t think they really understood it until this night.

“Magnus?” Alec asks after a moment, when the older man doesn’t respond, and his hand stops its gentle petting. Magnus has grown heavy while they talked, boneless in a way that betrayed deep weariness. Alec can feel the steady rise and fall of breath and realizes that Magnus fell asleep.

“I’ve got you,” Alec says, his tone quiet and fond, a small smile on his lips as he runs his thumb over the arch of Magnus’ brow. “And I’m not letting you go.”

**Author's Note:**

> Every fic is first posted to my tumblr and I upload it to AO3 with a delay. If you want to read my stories as soon as I finish them, follow me there: theonetruenorth.tumblr.com
> 
> Beta-read by [RomanceShipper](http://archiveofourown.org/users/RomanceShipper)


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